FIELD OF THE INVENTION
The present invention relates to a steam separator, a nuclear power generation plant, and a boiler apparatus equipped with a separator/injector having a two-phase flow accelerator nozzle for guiding a two-phase flow of mixed liquid and vapor components in the interior thereof and accelerating the same, a liquid-phase capture means for capturing the liquid phase of the thus accelerated two-phase flow, and means for increasing the pressure of this liquid phase and imparting a recirculation drive force thereto.
The description herein relates to nuclear power plants in general, taking a boiling-water reactor as an example with reference to the accompanying drawings.
Referring to FIG. 27, a reactor container 106 of a boiling-water reactor (BWR) is configured of a reactor pressure vessel 102 accommodating a core 101, a drywell 103 that contains this reactor pressure vessel 102, and a wetwell 105 having a pressure suppression pool 104. In addition, this nuclear power plant comprises a turbine 107, a main steam line 108 that supplies steam to that turbine 107, a main condenser 109, a condensate pump 110, a feedwater pump 111 that supplies feedwater to the reactor pressure vessel 102, a feedwater heater 112, a feedwater pipeline 113, a reactor recirculation system 114 that causes changes in the quantity of core coolant that recirculates therethrough, a control rod drive system 115 that controls the output, a standby coolant system 116 that operates when the reactor has been isolated by valves, a residual heat removal system that removes residual heat when the reactor is halted, and an emergency core coolant system (ECCS) that operates during emergencies.
Existing BWRs use a forced recirculation method by which coolant is sent through the core by the reactor recirculation system 114. This reactor recirculation system 114 is configured of a recirculation pump 117 and a jet pump 118. In an emergency, the recirculation pump 117 has a certain amount of inertia and takes about five seconds to stop, so the cooling efficiency of the coolant has to rely on a relatively weak natural circulatory system.
The ECCS is configured of a high-pressure core spray system 119 and a low-pressure core spray system 120 that also acts as the residual heat removal system. These operate together with a containment spray 121. The emergency core coolant system uses a condensate storage tank 122 or the pressure control pool 104 as a water source and supplies water into the core 101 by the rotation of a centrifugal pump driven by power supplied from emergency diesel generators 123, or sprays the water into the reactor container 106.
During an emergency, a boric acid solution is dumped in by an SLC (Standby Liquid Control System) pump 125 from a SLCS tank 124 into a lower plenum of the reactor pressure vessel.
In an advanced boiling-water reactor (ABWR), which is an improvement on the BWR, the external recirculation piping for the reactor recirculation system of the above described BWR is removed and recirculation through the core is enabled by the provision of a jet pump that is smaller than an internal pump, instead. The employment of an internal pump has various effects, such as a reduction in the pressure losses with respect to the flow of reactor coolant, in comparison with a BWR.
A cross-sectional view illustrating the concept of the systems of this ABWR is shown in FIG. 28. A core 52 that is provided with a large number of fuel rod assemblies is disposed slightly below the center of a reactor presure vessel 51. A large number of control rod guidance tubes 53 are provided below this core 52, and an upper aperture of a shroud 54 that shapes the core 52 is closed by a shroud head 55. Stand pipes 57 of steam separators 56 are erected above the shroud head 55, and flat, rectangular steam dryers 58 are disposed above the steam separators 56.
A control rod drive mechanism 59 is provided in a lower portion of the presure vessel 51, to drive the cross-shaped control rods within the core 52, using the inner surfaces of the control rod guide tubes 53. A plurality of internal pumps 60 are disposed in a base portion between the inner side of the reactor presure vessel 51 and the outer side of the shroud 54.
The core 52 is supported by a core support plate 61 that supports a lower portion of the large number of fuel rod assemblies, an upper portion thereof is supported by an upper lattice plate 62, and the entire core is surrounded by the shroud 54. A main steam line 108 that sends steam that has been dried by the steam dryers 58 to a turbine is connected to the reactor presure vessel 51. Coolant flowing into the reactor pressure 51 from a feedwater line 113 is recirculated by the internal pumps 60.
The reactor presure vessel 51 is mounted on and fixed to a pedestal, with a support skirt 63 therebetween. An upper aperture of the reactor presure vessel 51 is hermetically sealed by an upper lid 64.
A cross-sectional view of one of the steam separators 56 disposed within the reactor presure vessel 51 is shown in FIG. 29. This steam separator 56 comprises swirl vanes 41 provided above each of the stand pipes 57 to impart a swirling motion to a two-phase flow of steam-water mixtures, and steam separator stages 42a, 42b, and 42c provided above the swirl vanes in three consecutive stages in the axial direction as steam separator means for separating the steam from the two-phase liquid-vapor flow. Each of the steam separator stages 42a, 42b, or 42c has a double structure of a revolving tube 43a, 43b, or 43c with an outer tube 44a, 44b, or 44c positioned on the outer sides thereof. There is a hook-shaped pickoff ring 45a, 45b, or 45c formed on an upper portion of each of the outer tubes 44a, 44b, and 44c, respectively.
The description now turns to the operation of the steam separator 56. Coolant that has been boiled off by the heat of the fission reaction forms a two-phase liquid-vapor flow in which ordinary water and steam are mixed. It is distributed between the steam separators 56, which normally number between 200 and 300, and rises to the stand pipes 57. As shown in FIG. 29, the coolant within the stand pipes 57 forms a fluidized state called an annular flow. In other words, a liquid layer 48 covers the inner wall surface of each stand pipe 57 and a mixture of water droplets 49 and steam 50 flows within this liquid layer 48.
A centrifugal force is forcibly imparted to the two-phase flow rising through the stand pipe 57 by the swirl vanes 41 disposed directly above the stand pipe 57, to turn it into a rotating flow. At this point, the liquid-vapor density ratio of the coolant under normal operating conditions of the boiling-water reactor is 1:21, and thus a useful difference is generated in the centrifugal forces that are imparted by the rotational action to each of the vapor phase and the liquid phase.
This ensures that the low-density steam is positioned towards the center of the lowermost steam separator stage 42a, the high-density liquid forms the liquid layer 48 along the inner wall surface of the revolving tube 43a of this steam separator stage 42a, and both rise while rotating. This liquid layer 48 is carried upward along the inner wall of the revolving tube 43a against its own weight by the shear forces of the high-speed rotating flow near the center and is captured by the pickoff ring 45a which is a slit having a width that is designed to be substantially equal to the thickness of this liquid layer 48. Then, a thin annular portion between the concentric tubes 43a and 44a falls under its own weight. A breakdown ring 47 is provided partway along this flow path to prevent the intermixing of a large quantity of vapor bubbles, and the flow is sent on at a slower speed to an upper downcomer where it mixes with the surrounding liquid.
The larger part of the liquid phase that has not been captured by the lowermost steam separator stage 42a is captured by the pickoff rings 45b and 45c of the subsequent steam separator stages 42b and 42c.
Note that the apparatus is designed in such a manner that approximately 90% of the moisture extracted by the steam separator 56 from the steam passing through the steam separator 56 is removed by the lowermost steam separator stage 42a, and the mass ratio of water amidst the two-phase flow at the outlet of the steam separator 56 is suppressed to no more than 10%. More of the moisture in the steam that has passed through the steam separator 56 is removed by the steam dryer 58 disposed above each steam separator 56.
A steam injector has recently attracted attention as a static jet pump to be used instead of the prior-art rotary pump. This steam injector has a compact structure, requires no power source for operation, and can also be made to have a discharge pressure that is higher than the steam pressure at the inlet thereof.
An objective of the present invention is to make full use of the above characteristics in the application of a steam injector to a steam separator, to provide a steam separator which achieves substantially the same liquid-vapor separation effect as that of the above prior-art steam separator, and, at the same time, provide a higher discharge pressure.
The recirculation method currently used in BWRs and ABWRs necessitates components such as a large-scale pump, which is a rotating mechanism, and a large-capacity inverter power source for controlling that pump. From various viewpoints such as structural cost, material resources, and regularly scheduled maintenance, this method increases the cost of the plant and causes breakdowns in the rotating mechanisms. In contrast thereto, a movement has recently been seen to implement a simplified BWR with a modified natural recirculation method for the core that does not require jet pumps and internal pumps. Because the electrical output thereof is small in comparison to the size of the plant, the construction costs and unit-power costs tend to increase.
In a similar manner, it has become possible to design smaller, simpler equipment in pressurized water reactors (PWRs) and fast breeder reactors (FBRs) as well, by reinforcing the natural recirculation forces within steam generators. This is not limited to reactors; there is also a large demand for smaller, simpler installations having processes that separate out a liquid phase comprised within steam, such as boilers.